Master digital data creation device and digital data reproduction device

ABSTRACT

Data C generated by scrambling user-desired digital data P and a control word CW p  corresponding to the number of reproductions p are recorded on recording media. When creating a master, a user has already been charged for the number of reproductions p. A decryption block decrypts the control word CW p , which is read from the recording media, to CW 0 . A de-scrambler uses the decryption control word CW 0  to decrypt the digital data P for output to a reproduction unit. After confirming the end of reproduction, the decryption block writes a control word CW (p−1)  back to the recording media. The recording media may be reproduced p times with no need for communication between a reproduction device and an accounting manager.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a master digital data creationdevice and a digital data reproduction device, and more particularly toa master digital data creation device and a digital data reproductiondevice that prevent the illegal reproduction or copy of distributeddigital data such as audio data and video data.

[0003] 2. Description of the Related Art

[0004] Recently, more and more recording and reproduction devices andtheir media have become available for processing digital data. Thesedevices and media give audio and video users many benefits such ashigh-speed, non-degraded recording and reliable reproduction. On theother hand, a problem has arisen that many non-degraded copies areproduced quickly and sold with no permission from copyright holders. Theprevention of illegal copy has become critical.

[0005] To prevent illegal copy, the SCMS (Serial Copy Management System)is used for conventional digital recording and reproduction devices suchas a digital audio tape recorder (DAT) and a minidisk (MD). In the SCMS,copy permission status information is recorded in a particular area on amedium. That is, when the copy permission status information recorded ona copy source medium is “00”, the same copy permission statusinformation “00” is recorded also on a copy destination medium to permitthe user to create another copy from the copy destination medium (socalled copy free).

[0006] When the copy permission status information recorded on a copysource medium is “10”, the copy permission status information is changedto “11” on a copy destination medium to inhibit the user from creatinganother copy from the copy destination medium (that is, copy ispermitted only once). This system is established on the assumption that,upon detection of the copy permission status information of “11” on amedium, an SCMS-conforming device stops the copy operation.

[0007] Other conventional copy prevention methods include digital dataencryption. This is accomplished by scrambling copy-protecting digitaldata with the use of a predetermined control word and, at the same time,by encrypting the control word with particular key data.

[0008]FIG. 1 shows the overview of an exemplary conventional copyprotection method. In a mastering device 1 shown in the figure, ascrambler 2 scrambles digital data P, such as audio service (contents)data, using a control word P and outputs scrambled digital data C to arecording medium 4. At the same time, an encryption unit 3 encrypts thecontrol word P using key data K and outputs a control word C to therecording medium 4.

[0009] In a reproduction device 5, a decryption unit 6 receives thecontrol word C reproduced from the recording medium 4 and decrypts it tothe control word P using the key data K. At the same time, in thereproduction device 5, a de-scrambler 7 receives the digital data Creproduced from the recording medium 4 and produces the digital data Pusing the control word P already produced by the decryption unit 6.Algorithms suitable for this processing include DES(Data EncryptionStandard), RSA(named after Ron Rivest, Adi Shamir, and Len Adleman).When data is copied from this recording medium 4 to another recordingmedium, only the digital data C is copied, without the control word C.When reproducing data from the copy destination medium, de-scramblingprocessing cannot be performed correctly and therefore the user cannotreceive services (Digital data P cannot be reproduced correctly). Inthis way, the copy operation is virtually prevented.

[0010] However, when the copy permission status information is rewrittenin the SCMS, that is, when the information is altered, the followingproblem arises. For example, once the copy permission status informationon the copy source medium, even if “10”, is rewritten to “00” eitherwhen it is copied to a copy destination medium or by a processor on atransmission line, data may be illegally copied thereafter.

[0011] In addition, the conventional method for scrambling digital datain which all copies are prevented, the user is not permitted to createeven a personal backup copy against an accidental destruction of arecording medium. This is unreasonable because the merit of usingdigital data is impaired. What is important is that copy operationshould not be limited but that the copyright holder of digital contentsshould be paid for the service the user receives. This means that a copymanagement method other than that described above is required.

[0012] In the prior art, a method is disclosed which solves this problemby charging the user for the reproduction of digital contentsreproduction, calculating the total of the usage amount, anddistributing the charge among copyright holders (Japanese PatentLaid-Open Publication No. Hei 10-269289).

[0013] However, the conventional method and device, which return thedigital contents usage status to a charge manager, require communicationbetween the reproduction device and the charge manager and thereforemakes processing complex.

SUMMARY OF THE INVENTION

[0014] In view of the foregoing, it is an object of the presentinvention to provide a master digital data creation device and a digitaldata reproduction device capable of preventing illegal copies with noneed for communication between a reproduction device and a chargemanager.

[0015] To achieve the above object, there is provided a master digitaldata creation device comprising: an encryption block generating a firstcontrol word based on a specified allowable number of reproductions andapplying a one-way function to the first control word the allowablenumber of reproductions to generate a second control word; a scramblerreceiving the second control word for scrambling desired first digitaldata using the second control word to produce second digital data; andan output block outputting the second digital data and the first controlword to an external device.

[0016] According to the present invention, digital data, as well as thecontrol word including information on the allowable number ofreproductions, may be recorded on the recording media. Therefore, whenreproducing the digital data, the number times data may be reproducedmay be limited to the allowable number of reproductions. This simplifiesaccounting management and, at the same time, allows accountingprocessing for digital data copyright holders to be completed bycharging the user for a user-desired predetermined number ofreproductions the first time digital data is recorded on the recordingmedia, thus eliminating the need for communication with the accountingmanager for each reproduction.

[0017] To achieve the above object, there is provided a digital datareproduction device comprising: an acceptor accepting recording media onwhich second digital data and a first control word CW_(k) are recorded,the first control word being generated based on a specified allowablenumber of reproductions, the second digital data being generated byscrambling desired first digital data using a second control word CW₀generated by applying a one-way function to the first control wordCW_(k) K times; a decryption block receiving the first control wordCW_(k) and applying the one-way function to the first control wordCW_(k) k times to produce the second control work CW₀; a de-scramblerreceiving the second digital data and the second control word CW₀ andde-scrambling the second digital data using the second control word CW₀to produce the first digital data; and a reproduction unit reproducingthe first digital data generated by the de-scrambler, wherein, after thereproduction by the reproduction unit, the decryption block writes athird control word CW_((k−1)) back to the recording media, the thirdcontrol word being generated by applying the one-way function to thefirst control word CW_(k) once, and wherein, if the first control wordCW_(k) received from the recording media equals the second control wordCW₀, the de-scrambling by the de-scrambler and the reproduction by thereproduction unit are inhibited.

[0018] According to the present invention, when reproducing data fromthe recording media on which digital data and the control word includinginformation on the allowable number of reproductions are recorded, theallowable number of reproductions may be decremented for eachreproduction. Therefore, by inhibiting reproduction when the allowablenumber of times has reached 0, the number of times data may bereproduced may be limited to the allowable number of reproduction thatis initially set.

[0019] In a preferred embodiment of the present invention, when adesired number of reproductions, n, is received from some otherreproduction device, the decryption block receives the first controlword CW_(k) from the recording media and, if k ≧n, applies the one-wayfunction to the first control word CW_(k) (k−n) times to produce thethird control word CW_(n) and applies the one-way function to the firstcontrol word CW_(k) n times to produce the fourth control wordCW_((k−n)); if k<n, produces the first control word CW_(k) as the thirdcontrol word CW_(n) and produces the second control word CW₀ as thefourth control word CW_((k−n)); and records the fourth control wordCW_((k−n)) on the recording media for updating, further comprising: anoutput block outputting the second digital data recorded on therecording media, and the third control word CW_(n) obtained from thedecryption block, to the other reproduction device.

[0020] In this embodiment, when the number of reproductions, n, isspecified by some other reproduction device, the third control wordCW_(n), as well as the second digital data, is output to the otherreproduction device and, at the same time, the first control word CW_(k)is updated to CW_((k−n)). Therefore, a part of the limited number ofreproductions, k, is distributed from a reproduction device as a copysource to another reproduction device as a copy destination, connectedto the copy source, through the copy operation. This makes it possiblefor the number of reproductions to be managed independently when digitaldata is reproduced at the reproduction device as a copy source and atthe other reproduction device as a copy destination connected to thecopy source.

[0021] Therefore, the present invention allows digital data to bedistributed without impairing the merits of digital processing such ashigh-speed, non-degraded recording and reliable reproduction and, at thesame time, prevents illegal copy.

[0022] The nature, principle and utility of the invention will becomemore apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In the accompanying drawings:

[0024]FIG. 1 is an overview of an example of a conventional copyprevention method.

[0025]FIGS. 2A and 2B are a block diagram showing a digital datareproduction device in an embodiment according to the present inventionand a configuration diagram of main components, respectively.

[0026]FIG. 3 is a block diagram showing a master digital data creationdevice in the embodiment according to the present invention.

[0027]FIGS. 4A and 4B are a diagram depicting an example of theencryption block shown in FIG. 3 and the format of a control word,respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] An embodiment according to the present invention will bedescribed below with reference to the accompanying drawings.

[0029]FIG. 2A is a block diagram of an embodiment of a digital datareproduction device according to the present invention, and FIG. 2B is adiagram showing the configuration of the decryption block shown in FIG.2A. Before describing the digital data reproduction device in thisembodiment, the following describes how digital data that is the sourceof all copies (that is, master digital data) is created in anillegal-copy prevention system according to the present invention.

[0030]FIG. 3 is a block diagram of an embodiment of a master digitaldata creation device according to the present invention. In thedescription below, master digital data is simply referred to as amaster. Referring to FIG. 3, a master creation device 20 comprises ascrambler 21 scrambling digital data that is supplied to the user, anencryption block 22 encrypting a control word, and a communication block23 communicating with user's reproduction device. The communicationblock 23 is connectable to a reproduction device 25 via a transmissionmedium 24.

[0031] Next, referring to FIG. 3, the master creation operation will bedescribed. The master creation device 20 is installed, for example, in astore where video software and other software products are sold to theuser. The user goes to the store and connects his or her ownreproduction device 25 to the master creation device 20 via thetransmission medium 24. The user specifies digital data corresponding toa desired service and the number of reproductions p. Although not shownin this figure, the user is charged for the number of reproductions p.Note that the charge also depends on the digital data type, contents andso on.

[0032] The number of reproductions p is sent to the encryption block 22via the transmission medium 24 and the communication block 23 in themaster creation device 20. Although not required as input to theencryption block 22, key data K is also input to the encryption block 22to fully protect copyrights.

[0033] When the key data K is input to the encryption block 22, it isrequired that the same key data K be set also in the reproduction device25. The key data K may be used as input to a one-way function within theencryption block 22. The encryption block 22 outputs control word CW_(p)that depends on the number of reproductions p and control word CW₀ thatis input to the scrambler 21. The control word CW_(p) is sent to thereproduction device 25 via the communication block 23 and thetransmission medium 24.

[0034] The scrambler 21 uses the control word CW₀ to scramble digitaldata P selected according to the user's desire. Encryption algorithmssuch as the DES maybe used for scrambling. Digital data C, which isoutput from the scrambler 21 as a master, is sent to the reproductiondevice 25 via the communication block 23 and the transmission medium 24.The digital data C and the control word CW_(p) are recorded on therecording medium in the reproduction device 25. In this way, the userdesired digital data P that is scrambled, as well as the control wordCW_(p), is created in user's reproduction device 25 to produce arecording medium that may be reproduced the number of reproductions p.

[0035]FIG. 4A is an outline block diagram of an example of theencryption block 22 described above. This encryption block 22 firstgenerates a random value from a random value generator 221 to performreplacement. Because the number of reproductions is 3 in the example inFIG. 4A, a part of the random value is replaced with 3 according to theformat of the control word CW shown in FIG. 4B. The result is output asthe control word CW₃.

[0036] As shown in the format example in FIG. 4B, the control word CW iscomposed of a random value 27 of a one-way function f and a replacementvalue 28. The replacement value 28 indicates the number times theone-way function f is to be applied until the control word CW₀ isobtained. This is the number of times the one-way function is to beapplied until the control word CW₀ is obtained which is used to indicatethat the allowable number of reproductions has been exhausted in themaster digital data reproduction device or that a control word necessaryfor digital data de-scrambling has been obtained.

[0037] The control word CW3 described above is processed recursively bythe one-way function f the number of reproductions. The one-way functionf is defined as a function whose input is difficult to estimate from theoutput. The key data K, as well as the control word CW, is input to theone-way function f as necessary. The replacement operation is alsoperformed for the output of the one-way function f in each stage and,when the part of the control word CW eventually becomes 0, the controlword is output as CW₀. This control word CW₀ is used by the scrambler21.

[0038] Next, returning to FIGS. 2A and 2B, an embodiment of the digitaldata reproduction device will be described. As shown in FIG. 2A, areproduction device 10 is connected to another reproduction device 17via a transmission medium 16. This reproduction device 10 corresponds tothe reproduction device 25 shown in FIG. 3. The reproduction device 10comprises recording media 11 a and 11 b, a decryption block 12, ade-scrambler 13, a reproduction unit 14, and a communication block 15.On the recording medium 11 a, the data C sent from the master creationdevice 20 described above and generated by scrambling the user desireddigital data P is recorded. On the recording medium 11 b, the controlword CW_(p) corresponding to the number of reproductions P is recorded.

[0039] The de-scrambler 13 uses the control word CW₀, sent from thedecryption block 12, to de-scramble digital data from the recordingmedium 11 a to produce digital data P. The reproduction unit 14reproduces the received digital data P. The communication block 15 isprovided for communication between the reproduction device 10 and theother reproduction device 17 via the transmission medium 16.

[0040] As shown in the block diagram in FIG. 2B, the decryption block 12comprises a CW_(K) register 121 in which the control word CW_(K) readfrom the recording medium 11 b is temporarily stored, a CW_(n), register122 in which the control word to be output to the communication block 15is temporarily stored, a CW₀ register 123 in which the control word CW₀to be output to the de-scrambler 13 is temporarily stored, and a one-wayfunction f replacement processor 124. The one-way function f replacementprocessor 124 receives the number of reproductions n from thereproduction device 17.

[0041] Next, the operation of the embodiment shown in FIGS. 2A and 2Bwill be described. The digital data C, such as audio service datascrambled by the master creation device 20 with the use of the controlword CW₀, is input to the reproduction device 10 for recording on therecording medium 11 a. At the same time, the control word CW_(p)corresponding to the number of reproductions p is input to thereproduction device 10 for recording on the recording medium 11 b.

[0042] The control word CW_(p) recorded on the recording medium 11 b isread into the decryption block 12, where the control word CW_(p) isdecrypted to the control word CW₀ using the same keyword K as that usedby the master creation device 20. The control word CW₀, in conjunctionwith the digital data C read from the recording medium 11 a, is input tothe de-scrambler 13. The de-scrambler 13 de-scrambles the receiveddigital data C using the decryption control word CW₀ and outputs thede-scrambled digital data P to the reproduction unit 14.

[0043] The reproduction unit 14 decodes the encoded digital dataPreceived from the de-scrambler 13 and outputs the decoded data to adevice external to the reproduction device 10 for providing the serviceto users. After confirming that reproduction has been terminated, thedecryption block 12 writes the control word CW_((p−1)) back to therecording medium 11 b.

[0044] Next, copying the digital data C from the recording medium 11 ato a recording medium on another reproduction device 17 will bedescribed. In this case, the other reproduction device 17 first informsthe reproduction device 10 of the desired number of reproductions, n,via the communication block 15. Assume that the control word currentlyrecorded on the recording medium 11 b is CW_(K). The decryption block 12reads this control word CW_(K) from the recording medium 11 b andrecursively performs the one-way function and replacement for thiscontrol word to output the control word CW_(n).

[0045] The control word CW_(n) output from the decryption block 12, inconjunction with the digital data C read from the recording medium 11 a,is supplied, via the communication block 15 and the transmission medium16, to the other reproduction device 17 for copying the data to itsrecording medium. After confirming that a copy is created successfully,the decryption block 12 updates the contents of the recording medium 11b with the control word CW_(k)′ generated by recursively performing theone-way function and replacement for the control word CW_(k). Note thatk′=k−n. That is, because a copy permitting n times of reproductions ismade from the recording media 11 a and 11 b, from which data may becopied up to k times, to the other reproduction device 17, the remainingnumber of reproductions of the recording media 11 a and 11 b equals(k−n) times.

[0046] Next, processing performed by the decryption block 12 will bedescribed more in detail. Assume that the control word recorded on therecording medium 11 b is CW₅ (K=5). That is, in the description below,it is assumed that digital data that may be reproduced up to five timeswill be copied once. In this case, the decryption block 12 reads thecontrol word CW₅ from the recording medium 11 b and temporarily storesit in the CW_(K) register 121 in the decryption block 12.

[0047] Next, the processor 124 performs the one-way function f andreplacement for the control word CW5 in the CW_(K) register 121 once andstores the result in the CWK register 121 to update its contents. Theone-way function f and replacement processing are the same as thoseperformed by the encryption block 22 shown in FIG. 4A. That is, theCW_(K) register 121 contains CW₄ at this time.

[0048] After that, the processor 124 performs the one-way function f andreplacement repeatedly and, when the result becomes CW₀, stores thiscontrol word CW₀ in the CW₀ register 123. Finally, the contents of theCWK register 121 are written back to the recording medium 11 b, and thecontents of the CW₀ register 123 are output to the de-scrambler 13.

[0049] Next, the following describes how digital data is copied when thecontrol word recorded on the recording medium 11 b is CW₅ (k=5), thatis, when data may be reproduced up to five times, and the number ofreproductions of 2 is specified (n=2). In this case, the decryptionblock 12 reads the control word CW₅ from the recording medium 11 b andtemporarily stores it in the CW_(K) register 121 in the decryption block12.

[0050] Then, the processor 124 performs the one-way function f andreplacement for the control word CW₅, stored in the CW_(K) register 121,(k−n) times to produce the control word CW_(n) and stores it in theCW_(n) register 122. When n=2, the control word CW₂ is stored in theCW_(n) register 122.

[0051] In addition, the processor 124 performs the one-way function fand replacement for the control word CW₅, stored in the CW_(K) register121, n times to produce the control word CW_((k−n)) and stores it in theCW_(k) register 121 to update its contents. When n=2, the control wordCW₃ is stored in the CW_(K) register 121. That is, the remainingallowable number of reproductions is 3 (=5−2).

[0052] After that, the processor 124 performs the one-way function f andreplacement repeatedly and, when the result becomes CW₀, stores thiscontrol word CW₀ in the CW₀ register 123. Finally, the control word CW₂stored in the CW_(n) register 122 is output to the communication block15 and then the contents (CW₃) of the CW_(K) register 121 are writtenback to the recording medium 11 b.

[0053] Next, the following describes how digital data is copied when thecontrol word recorded on the recording medium 11 b is CW₅ (k=5), thatis, when data may be reproduced up to five times, and the number ofreproductions of 6 is specified (n=6). In this case, too, the decryptionblock 12 reads the control word CW₅ from the recording medium 11 b andtemporarily stores it in the CW_(K) register 121 in the decryption block12.

[0054] In this case, because k−n=5−6=−1(≦0), the processor 124 does notperform processing for the control word CW₅, with the control word CW₅remained in the CW_(n) register 122.

[0055] In addition, because k−n=5−6=−1(≦0), the processor 124 performsthe one-way function f and replacement for the control word CW₅, storedin the CW_(K) register 121, maximum times, namely, five times to producethe control word CW₀ and stores it in the CW_(K) register 121 to updatesits contents. That is, the remaining allowable number of reproductionsbecomes 0. The control word CW₀ is stored in the CW₀ register 123.

[0056] Finally, the control word CW₅ stored in the CW_(n) register 122is output to the communication block 15 and then the contents (CW₀) ofthe CW_(K) register 121 are written back to the recording medium 11 b.After that, when the recording media 11 a and 11 b are reproduced, thecontrol word CW₀ is reproduced from the recording medium 11 b andtherefore the decryption block 12 does not decode data and reproductionis not performed normally. As described above, even if the number ofreproductions larger than the allowable number of reproductions isspecified in this embodiment, only the allowable number of reproductionsmay be made and an attempt to create more copies than the allowablenumber of reproductions is prevented.

[0057] It should be understood that many modifications and adaptationsof the invention will become apparent to those skilled in the art and itis intended to encompass such obvious modifications and changes in thescope of the claims appended hereto.

What is claimed is:
 1. A master digital data creation device comprising:an encryption block generating a first control word based on a specifiedallowable number of reproductions and applying a one-way function to thefirst control word the allowable number of reproductions to generate asecond control word; a scrambler receiving the second control word forscrambling desired first digital data using the second control word toproduce second digital data; and an output block outputting the seconddigital data and the first control word to an external device.
 2. Adigital data reproduction device comprising: an acceptor acceptingrecording media on which second digital data and a first control wordCW_(k) are recorded, said first control word being generated based on aspecified allowable number of reproductions, said second digital databeing generated by scrambling desired first digital data using a secondcontrol word CW₀ generated by applying a one-way function to the firstcontrol word CW_(k) k times; a decryption block receiving the firstcontrol word CW_(k) and applying the one-way function to the firstcontrol word CW_(k) k times to produce the second control work CW₀; ade-scrambler receiving the second digital data and the second controlword CW₀ and de-scrambling the second digital data using the secondcontrol word CW₀ to produce the first digital data; and a reproductionunit reproducing the first digital data generated by said de-scrambler,wherein, after the reproduction by said reproduction unit, saiddecryption block writes a third control word CW_((k−1)) back to saidrecording media, said third control word CW_((k−1)) being generated byapplying the one-way function to the first control word CW_(k) once, andwherein, if the first control word CW_(k) received from the recordingmedia equals the second control word CW₀, the de-scrambling by saidde-scrambler and the reproduction by said reproduction unit areinhibited.
 3. The digital data reproduction device according to claim 2, wherein, when a desired number of reproductions, n, is received fromsome other reproduction device, said decryption block receives the firstcontrol word CW_(k) from the recording media and, if k≧n, applies theone-way function to the first control word CW_(k) (k−n) times to producethe third control word CW_(n) and applies the one-way function to thefirst control word CW_(k) n times to produce the fourth control wordCW_((k−n)); if k<n, produces the first control word CW_(k) as the thirdcontrol word CW_(n) and produces the second control word CW₀ as thefourth control word CW_((k−n)); and records the fourth control wordCW_((k−n)) on the recording media for updating, further comprising: anoutput block outputting the second digital data recorded on therecording media, and the third control word CW_(n) obtained from thedecryption block, to the other reproduction device.